equine health

My trainer mentioned the other day that B could benefit from some Vitamin E. I'm searching the KV Vet Supply Catalog and am totally overwhelmed by the choices, plus I know that some aren't absorbed as well as others. I don't take vitamins myself, and I know some people believe that a complete feed, plus good hay and pasture are all a horse really needs. But B's in heavy training.
What do you think? Supplements? Opinions desired!